Set SSH keys automagically when running `new`

This changeset introduces the ability to send SSH keys to remote hosts when running `ceph-deploy new`.

A few things worth noting:

* It will attempt to SSH to the remote host using `Batchmode=yes` which exits immediately to prevent a password prompt signaling the need for SSH keys to be setup.

* Allows a `--no-ssh-copykeys` flag to skip this sort of magic being triggered

* Will use the current user's `id_rsa.pub` file if that exists, otherwise it will create them with an empty passphrase and use those in turn to copy them over.

* Full docs are forthcoming.